Self-adhesive material of hydrogenated block copolymers and protective film for smooth surfaces made thereof

ABSTRACT

The invention relates to the self-adhesive material of hydrogenated block copolymers or a mixture thereof, comprising polymer blocks of vinyl aromatics (A-blocks) and such made by polymerization of 1,3 dienes (B-blocks), mixing the self-adhesive material with 10 to 80 parts per weight, preferably with 10 to 40 parts per weight polyisobutylene with an average molecular weight M w  in relation to 100 parts by weight M w  of the blockcopolymeres.

The invention relates to a self-adhesive composition comprisinghydrogenated block copolymers and also to the use thereof in protectivefilms which adhere securely to smooth surfaces and can be removed fromthem easily and without residue even after UV exposure.

Heightened requirements in the design of articles of everyday use arecontinually giving rise to new, sensitive surfaces, and the modernconsumer expects a flawless product on purchase.

The sensitive surfaces of many consumer goods are therefore protectedwith surface-protection films, which protect them effectively from minormechanical events and help to prevent value-reducing marring anddulling. Surface-protection films are generally composed of a backingfilm, which develops the actual protective effect, and a self-adhesivecomposition, which on the one hand fixes the film securely to thearticle to be protected, from the outset, and on the other hand mustensure easy and traceless releasability.

The conditions to which the protected surface and the protective filmare exposed may be very different depending on the article and itsintended use. In practice these conditions range from a bonding time ofjust a few hours under normal ambient conditions, as during assembly,for instance, through to months-long bonding times under adverseconditions, including UV exposure or high atmospheric humidity.

The necessary bond strength of the protective film depends on thesubstrate material and on the nature of its surface. This surface may beglossy or matt, or smooth or variously textured. No onesurface-protection product covers all of the requirements. This explainsthe multiplicity of surface-protection film products that are on offer.

Dominating the sector are protective films with a carrier made frompolyolefins and with self-adhesive compositions made from acrylic esterpolymers, applied both from solution and from aqueous dispersion. Thetack of the acrylic ester polymers can be given a variety offormulations, and for numerous applications they also function entirelyproperly. In general, however, the relatively polar acrylic esterpolymers tend to exhibit peel increase on the substrate—that is, toincrease the strength of their adhesion to the substrate over time ascompared with the initial level of adhesion.

Likewise widespread are black/white polyolefin films which are coloredwhite on the outside and black beneath and are usually combined withnatural-rubber self-adhesive compositions. This film, which is opaque tolight, is intended to protect the light-sensitive natural-rubberself-adhesive composition from light-induced decomposition, which wouldlead automatically to intolerable residues of adhesive.

This type of protective film is employed especially when acrylic esterpolymers are not suitable; in other words, when their polar nature leadsto severe interaction with the substrate, which is frequently the caseon PVC, for example, such as window profiles. Generally speaking,natural-rubber self-adhesive compositions are the more suitableself-adhesive compositions for surface protection, since they arenonpolar and have less of a tendency toward peel increase than acrylicester polymers. Their substantial drawback is the instability to light,which can be compensated only by means of a film which is opaque tolight but which, consequently, is less attractive. On optical grounds orelse on practical grounds, a transparent protective film is sometimesmore desirable, since the area covered can be viewed.

In many cases, therefore, a film that would be advantageous would be afilm combining a transparent carrier with a nonpolar natural-rubberself-adhesive composition.

One solution may be the use of synthetic rubbers which, incontradistinction to natural rubber, are in some cases also available ina hydrogenated and therefore more light-stable form. Nevertheless,natural rubber cannot be swapped directly for a synthetic rubber;synthetic-rubber compositions must overall be given a differentformulation.

One attempt in this direction is disclosed in WO 03/18702 A1, wherepreference is given to using styrene block copolymers, which may also behydrogenated, together with tackifier resins and polymeric plasticizercomprising polyisobutylene, which must have a softening temperaturebelow 25° C. and is therefore liquid at room temperature. Although, asquoted, the protective film does function on a number of paintedsurfaces, it is nevertheless the case that on numerous substrates,particularly after exposure to temperature, residues of adhesive areobserved which indicate inadequate cohesion of the composition.

WO 03/018701 A1 discloses a self-adhesive protective film forsurface-protection applications which has a single-ply or multi-plycarrier layer, more particularly a polyolefinic carrier layer, and aself-adhesive layer. The construction of the self-adhesive compositionis as follows:

-   -   30% to 70% by weight of one or more elastomers based on block        copolymers, including polymer blocks formed from vinylaromatics        (A blocks), preferably styrene, and polymer blocks formed by        polymerization of 1,3-dienes (B blocks), preferably butadiene        and isoprene and/or their hydrogenation products, and also    -   30% to 70% by weight of tackifier resins, at least half of the        tackifier resins being liquid resins having a softening point of        below 25° C. as measured using the ring and ball method.

EP 1 388 582 A1 discloses a self-adhesive protective film whoseself-adhesive composition is based on a polyisobutylene and/or a styreneblock copolymer. More precise details concerning the type ofpolyisobutylene or its molecular weight, and also concerning mixingratios, are absent. This suggests that any conceivable mixing ratios orany polyisobutylenes form a suitable self-adhesive composition for asurface-protection film. It is indeed possible to find mixing ratioswhich adhere too strongly or too weakly. With polyisobutylenes which areliquid at room temperature, the cohesion can become too low, as alreadyobserved above. If the fraction of styrene block copolymer is too great,then irreversible imprints of creases, bubbles or the edges of the filmare observed on sensitive substrates such as paints.

It is an object of the present invention to provide a self-adhesivecomposition comprising hydrogenated block copolymers, and a protectivefilm produced using said composition, that does not have thedisadvantages of the prior art, or not to the same extent. Inparticular, the proposed self-adhesive composition comprisinghydrogenated block copolymers ought to have a light stability such thatit can be used, in particular, on transparent carrier films, so that aprotective film for smooth substrates can be provided that is composedof a transparent carrier film and the self-adhesive composition of theinvention, said film not harboring the risk of premature, light-induceddecomposition of adhesive, and at the same time playing out theadvantages of nonpolar, rubberlike self-adhesive compositions.

This object is achieved by means of a self-adhesive composition of thekind recorded in the main claim. The dependent claims provideadvantageous developments of the self-adhesive composition, and also aprotective film produced using it.

The invention accordingly provides a self-adhesive compositioncomprising hydrogenated block copolymers or a mixture of such,comprising polymer blocks formed from vinylaromatics (A blocks),preferably styrene, and polymer blocks formed by polymerization of1,3-dienes (B blocks), preferably butadiene and isoprene and/or theirhydrogenation products. The self-adhesive composition is blended with 10to 80 parts by weight, preferably with 10 to 40 parts by weight, ofpolyisobutylene having a weight-average molecular weight M_(w)>200 000g/mol, based on 100 parts by weight of the block copolymers.

Elastomers employed include those based on block copolymers includingpolymer blocks formed by vinyl-aromatics (A blocks), preferably styrene,and polymer blocks formed by polymerization of 1,3-dienes (B blocks),preferably butadiene and isoprene, and preferably their hydrogenatedderivatives. Both homopolymer blocks and copolymer blocks can beutilized in accordance with the invention. Resultant block copolymersmay contain identical or different B blocks. Block copolymers can have alinear A-B-A structure; likewise possible for use are block copolymersof radial design and also star-shaped and linear multiblock copolymers.Further components present may include A-B diblock copolymers. Blockcopolymers of vinylaromatics and isobutylene are likewise possible foruse in accordance with the invention. All of the aforementioned polymersmay be utilized alone or in a mixture with one another.

Instead of the polystyrene blocks it is also possible to utilize polymerblocks based on other aromatics-containing homopolymers and copolymers(preferably C₈ to C₁₂ aromatics) having glass transition temperaturesof > about 75° C., such as a-methylstyrene-containing aromatics blocks,for example.

Instead of styrene-butadiene block copolymers and styrene-isoprene blockcopolymers and their hydrogenation products, includingstyrene-ethylene/butylene block copolymers andstyrene-ethylene/propylene block copolymers, it is likewise possible inaccordance with the invention to utilize block copolymers and theirhydrogenation products which utilize further polydiene-containingelastomeric blocks, such as, for example, copolymers of two or moredifferent 1,3-dienes. Further suitable for use in accordance with theinvention are functionalized block copolymers, such as maleicanhydride-modified or silane-modified styrene block copolymers, forexample.

In one outstanding embodiment of the invention the elastomers arehydrogenated predominantly in the middle block, and in particular arehydrogenated completely in the middle block.

The polyisobutylenes are homopolymers of isobutene and by their natureare relatively insensitive to the effects of light, since they containno unsaturated bonds. The polyisobutylenes are available commercially innumerous molecular weights. Typically, polyisobutenes havingweight-average molar masses of from M_(w)=30 000 g/mol up to more than 4000 000 g/mol are offered. Below a weight-average molar mass of aboutM_(w)=200 000 g/mol, the polyisobutylenes are liquid at roomtemperature; above that molar mass, they are rubberlike. In the lattercase they can be brought into a readily processible form by granulation.

Only polyisobutylenes having a weight-average molar mass of aboveM_(w)=200 000 g/mol have proved to be suitable as an addition tohydrogenated block copolymers in the sense of the invention, since onlyin that case is the cohesion sufficient even under demanding conditions.

The amount of polyisobutylenes with weight-average molecular weightM_(w)>200 000 g/mol that is used is 10 to 80 parts by weight, preferably10 to 40 parts by weight, of polyisobutylene per 100 parts by weight ofblock copolymer. Within these proportions, the adhesion to thesubstrates is raised to a considerable degree in relation to pure blockcopolymers. The desired synthetic-rubber character of the blockcopolymers is retained.

As further additives in the adhesive formulation it is possibletypically to utilize the following:

-   -   primary antioxidants such as, for example, sterically hindered        phenols    -   secondary antioxidants such as, for example, phosphites or        thioethers    -   in-process stabilizers such as, for example, C-radical        scavengers    -   light stabilizers such as, for example, UV absorbers, sterically        hindered amines    -   processing assistants    -   fillers

The hydrogenated block copolymers and the polyisobutylene can bedissolved homogeneously, in all proportions in accordance with theinvention, in suitable solvents such as, for example, toluene ortoluene/benzine mixtures. These solutions can be coated out in anydesired thickness onto carrier materials, and freed from the solvent byexposure to heated, moving air.

The components of the self-adhesive composition of the invention canalso be mixed solventlessly, for example, in an internal mixer or, in amelted form, in suitable assemblies such as, for example, extruders orcompounders. They may also be formed to a film, solventlessly, incalenders or extruders with a slot die, for example, and applied to thecarrier web.

The self-adhesive composition of the invention is also suitable forbeing shaped simultaneously with the carrier in a multi-ply coextrusionprocess to give a completed surface-protection film.

These properties by themselves support the use of the adhesive of theinvention on a carrier film which ultimately can be used for theprotection of surfaces. The general expression “protective film”encompasses, for the purpose of this invention, all sheetlike structuressuch as two-dimensionally extended films or film sections, tapes withextended length and limited width, tape sections, die cuts, labels, andthe like. The desire most often is for flexible protective films whichcan easily conform to the contors of the substrate by extending. In thiscase, the protective film produced from the adhesive of the inventionhas a carrier preferably comprising polyolefins. These may be, forexample, polyethylene, polypropylene, and also blends or copolymersthereof (for example, random copolymer or polypropylene blockcopolymer).

In order to set particular mechanical properties such as toughness,flexibility, adhesion to the adhesive, extrusion behavior orparticularly smooth surface structure, the films may also includedifferent amounts of further polyolefin copolymers such as copolymers ofethylene and α-olefins such as 1-butene, 1-hexene, 1-octene (calledLLDPE, VLDPE or ULDPE, or metallocene-PE, according to fraction andpreparation process), but also ethylene-styrene copolymers, ethylenewith polar comonomers such as acrylic acid or vinyl acetate, andcopolymers of propylene with α-olefins, such as ethylene, 1-butene,1-hexene, 1-octene. Likewise suitable are PVC films, especiallyplasticized PVC films.

In some cases the desire is for dimensionally stable protective filmswhich should not stretch when being applied or removed. In that casefilms that are employed are those comprising monoaxially or biaxiallyoriented polyolefins or comprising polymers with a high elasticitymodulus, such as, for example, polystyrene, polycarbonate, polyamide,polyesters (polyethylene terephthalate, polybutylene terephthalate) orpolymethyl methacrylate. Also embraced by the concept of the inventionare film composites made of different layers of materials.

In one advantageous development of the invention the thickness of thecarrier film is between 20 and 80 μm. The invention is aimedparticularly at light-stable protective films. In order to give thecarrier film the requisite UV stability, the addition of lightstabilizers is preferred. Their function consists primarily in theavoidance of embrittlement of the carrier film. Light stabilizers ofthis kind are described in Gaechter and Müller, Taschenbuch derKunststoff-Additive, Munich 1979, in Kirk-Othmer (3rd) 23, 615 to 627,in Encycl. Polym. Sci. Technol. 14, 125 to 148, and in Ullmann (4th) 8,21; 15, 529, 676. HALS light stabilizers in particular are suitable forthe polyolefinic carrier materials. The amount of the light stabilizerought to be at least 0.15% by weight, preferably at least 0.30% byweight, based on the carrier film.

The use of antioxidants for the film (for example, Irganox 1010 ortrisnonyiphenyl phosphite), though advantageous, is not mandatory.Further suitable UV absorbers, light stabilizers, and aging inhibitorsare listed in EP 0 763 584 A1.

Although transparency is often desired, there are cases where, forreasons of recognition or light shielding, the requirement is foropacity or even imperviousness to light. In these cases the carrier maybe filled with opaque fillers such as titanium dioxide or carbon black.This ensures opacity and a further improvement in the light stability ofthe carrier film.

In order to scavenge metals which catalyze decomposition it is possiblethat metal deactivators, which are integrated in the carrier film, areadvantageous, including hydrazines and hydrazides.

Optical design is served using dyes or color pigments, both alone and inconjunction with fillers, in order to obtain colored transparency,translucency or opaque color.

Lubricants and antiblocking agents such as erucamide, oleamide, andglyceryl monostearate, and also acid scavengers such as calcium stearateand other metal soaps, can be employed, with the proviso that they donot adversely affect the adhesive properties of the self-adhesivecomposition, through migration or transfer from the reverse of thecarrier film to the self-adhesive composition.

To reduce the cost of the film, or in order to achieve particularproperties, it is also possible to employ other fillers such as chalk ortalc.

The preferred polyolefin films are produced by the relevantly knownmethods, such as the chill roll method, in which the melt emerging froma slot die is cast onto a chill roll, on which the melt solidifies toform a film. Another widespread method is the blown film method, inwhich the melt is extruded as a parison from an annular die and inflatedto a greater or lesser extent in order to obtain the desired dimensions(thickness and diameter) of the parison.

If necessary, the anchorage of the self-adhesive composition on thecarrier film may be enhanced by coating with a primer or with a layer ofadhesion promoter, as an aid to anchorage. This purpose may also beserved by corona pretreatment or flame pretreatment of the side of thefilm that is to be coated.

On the reverse of the protective film it is possible, if necessary, fora reverse-face varnish to be applied in order to promote the unwindproperties of the protective film wound to an Archimedean spiral. Thisreverse-face varnish may for that purpose be equipped with siliconecompounds or fluorosilicone compounds and also with polyvinylstearylcarbamate, polyethylenimine stearylcarbamide or organofluorinecompounds as abhesive substances.

In the case of multi-ply coextrusion it is advantageous to coextrude thelayer comprising the release agent with the overall construction.

The self-adhesive composition of the invention is distinguished by agood initial force of adhesion to smooth and in particular to glossysubstrates. The adhesiveness increases in the course of storage for aprolonged period, even at elevated temperature, to a slight degree.

The protective film produced therefrom, even in conjunction with alight-transmitting carrier film, exhibits good light stability formonths. Even after exposure to heat and sunlight, it can be detachedeasily and without residue from the substrate. In this context, thesubstrate does not undergo any change in appearance such as yellowing,alteration in gloss, or instances of swelling.

On account of the unexpected positive properties, the self-adhesivecomposition can be used in a protective film which can be employed onfreshly painted surfaces of vehicles such as automobiles, or automobileparts, as assembly protection or transit protection, or else can be usedfor protecting smooth paint, metal, plastic or glass surfaces.

The self-adhesive composition of the invention and thesurface-protection films produced from it are described below in apreferred version, on the basis of a number of examples, without anyintention that the invention should thereby likewise be subject to anyrestriction whatsoever.

Also given are comparative examples, which show unsuitable self-adhesivecompositions and protective films produced from them.

EXAMPLES

All self-adhesive compositions for the production of specimens wereprepared by weighing in the components of the composition and dissolvingthem in the toluene solvent at a solids concentration of 20%. Theself-adhesive compositions were coated out using a laboratory coatingmachine on a corona-pretreated, colorlessly transparent LDPE film 50 μmthick, light-stabilized with 0.2% of Chimassorb 944(poly[[6-[(1,1,3,3-tetramethylbutyl)amino]-s-triazine-2,4-diyl]-[(2,2,6,6-tetramethyl-4-piperidyl)imino]hexamethylene-[(2,2,6,6-tetramethyl-4-piperidyl)imino]],a HALS light stabilizer from CIBA) in a coat thickness such that dryingin a drying cabinet at 95° C. for 4 minutes gave an adhesive coat weightof 10 g/m².

After cooling, the specimens were lined with a siliconized release filmand after a waiting time of not less than 48 hours were slit to formstrips 20 mm wide. The tests described below were carried out usingthese strips.

Assessment Criteria

The criteria for an application-compatible self-adhesive composition forsurface-protection films are

-   -   sufficient instantaneous adhesion    -   a moderate increase in bond strength after temperature exposure    -   a moderate increase in bond strength and residue-free        removability after UV exposure    -   no surface alterations after demasking.

This is elucidated in more detail below:

Instantaneous Adhesion

Sufficient instantaneous adhesion on the substrate to be protected mustbe provided, so that the surface-protection film is easy to apply andadheres securely from the outset. One measure of this is theinstantaneous bond strength, in other words the force needed to peel thesurface-protection film from the substrate again directly afterapplication.

Peel Increase

So that the substrate to be protected can be easily demasked again, theself-adhesive surface-protection film must not exhibit excessive peelincrease; in other words, the difference between the peel strength aftera long period of bonding and the instantaneous bond strength must not betoo great. This is all the more important given that surface-protectionfilms are frequently employed in large dimensions and hence the forceexpended for demasking can be considerable.

Surface Alteration

A surface-protection film shall protect the substrate from damage orsoiling, but must not alter the substrate itself.

Discoloration and irreversible deformation of the surface, in the formof an imprint of creases or film structures incorporated in the bondingprocess, are unwanted, as are adhesive residues and deposits.

UV Stability

The effect of UV light on the self-adhesive surface-protection film mustinclude neither embrittlement or tearing of the carrier on demasking,nor detriment to the cohesion of the self-adhesive composition such thatthere are residues on the substrate.

Implementation of the Tests, and Evaluation Schemes

The specimens, slit to strips, were applied to various representativesubstrates, and the bond strength was determined by means of a tensiletesting machine, both instantaneously and after different stresses.

Particular attention was paid here to the assessment of the substrateafter demasking.

Instantaneous Adhesion

The instantaneous adhesion was measured by a method based on the ASTMD3330 bond strength measurement method, on smooth test plaques producedfrom polycarbonate (PC), unpiasticized polyvinyl chloride (PVC),acrylonitrile-butadiene-styrene copolymer (ABS), window glass (glass),and one-component polyurethane varnish (1K PU varnish). The peel anglewas 180° and the peel speed 300 mm/min. The bond strength was measuredwithin five minutes after bonding.

An instantaneous adhesion of 0.2 N/cm or more was evaluated as good.

Peel Increase

A long bonding time was simulated by thermal exposure of the specimensbonded to the substrates, at an elevated temperature of 80° C. for sixdays. After the heat-exposed specimens had cooled to room temperature,the peel force was measured by a method based on the ASTM D3330 bondstrength measurement method. The peel increase (A) is calculated as thedifference in peel force after thermal exposure and instantaneousadhesion.

An increase in the peel force by not more than 1 N/cm was evaluated asgood.

Independently of the peel increase, a peel force after thermal exposureof more than 2 N/cm was evaluated as negative.

Instantaneous Adhesion

After the thermally exposed specimens had been removed by peeling, thearea of former bonding was inspected. The assessment was positive(satisfactory, OK) if there were no visible changes apparent to thesubstrate.

UV Stability

The UV stability was tested by exposure to UV light in the Q-panelQUV/SE weathering instrument. The radiation output was 0.92 W/m²/nm,which is achieved using lamp type UVA-340. For this test, the irrigationunit was not in operation.

At regular intervals of approximately 24 hours, the specimens weredemasked and the substrate was inspected for residues, as a sign ofincipient weakness in cohesion.

The specimens were evaluated as being sufficiently UV-stable if noresidues of adhesive were apparent after at least 400 h of UV exposure.

Molecular Weight Determination

The molecular weight determinations of the weight-average molecularweights M_(w) took place by means of gel permeation chromatography(GPC). The eluent used was THF (tetrahydrofuran) with 0.1% by volumetrifluoroacetic acid. Measurement took place at 25° C. The preliminarycolumn used was PSS-SDV, 5μ, 10³ Å, ID 8.0 mm×50 mm. Separation wascarried out using the columns PSS-SDV 5μ, 10³ and also 10⁵ and 10⁶, eachof ID 8.0 mm×300 mm. The sample concentration was 4 g/l, the flow rate1.0 ml per minute. Measurement was carried out against PMMA standards.

Formulas of the Examples and Counterexamples

In accordance with the invention, the self-adhesive compositionsselected to illustrate the invention are composed of hydrogenated blockcopolymers and polyisobutylenes. The numbers in the examples andcounterexamples indicate the parts by weight of the components in theformulation. M_(w) designates the weight-average molecular weight.

EXAMPLES

Substance Type E-1 E-2 SEPS Septon 2063 (Kuraray) 100 SEBS G-1657(Kraton) 100 PIB (M_(w) = 340 000 g/mol) Oppanol B50 (BASF) 25 25 PIB(M_(w) = 36 000 g/mol) Oppanol B10 (BASF)

Septon 2063 is an SEPS with a styrene content of 13% by weight and withan average molecular weight M_(w) of 65 000.

The Kraton G-1657 is an SEBS likewise with a styrene content of 13% byweight, and with a diblock content of 30% and an average molecularweight M_(w) of 100 000.

Counterexamples

Substance Type C-1 C-2 SEPS Septon 2063 (Kuraray) SEBS G-1657 (Kraton)100 100 PIB (M_(w) = 340 000 g/mol) Oppanol B50 (BASF) 150 PIB (M_(w) =36 000 g/mol) Oppanol B10 (BASF) 25

Test Results

Substrate E-1 E-2 C-1 C-2 Instantaneous adhesion (in N/cm) PC 1.0 1.11.5 1.5 PVC 0.8 0.7 1.0 1.0 ABS 0.7 0.6 1.2 0.7 glass 0.8 0.9 0.9 0.9 1KPU varnish 0.5 0.3 0.9 0.6 Bond strength after thermal exposure (inN/cm) PC 1.7 1.9 2.9 2.7 PVC 1.3 1.5 2.2 2.3 ABS 1.6 1.5 2.7 2.5 glass0.6 0.5 0.7 1.0 1K PU varnish 1.4 1.0 1.7 2.1 Peel increase Δ (in N/cm)PC 0.7 0.8 1.4 1.2 PVC 0.5 0.8 1.2 1.3 ABS 0.9 0.9 1.5 1.8 glass −0.2−0.4 −0.2 0.1 1K PU varnish 0.9 0.7 0.8 1.5 Surface assessment afterthermal exposure PC OK OK MR MR PVC OK OK MR MR ABS OK OK MR MR glass OKOK slight B OK 1K PU varnish OK OK MR OK UV stability (time untilappearance of residues, in hours) glass 663 708 141 615

Abbreviations:

OK = no visible alteration to the surface B = deposit on the substrateMR = residues of adhesive D = substrate deformation

Example E-1 and E-2 exhibit an application-compatible profile ofproperties, exhibiting a sufficient instantaneous bond strength of insome case well above 0.2 N/cm, and achieving a moderate peel increase ofless than 1 N/cm after temperature storage. A value of 2 N/cm is notexceeded. The surfaces of the substrates have not altered as a result ofthe temperature storage; demasking was possible without residue. At wellover 400 hours, the UV stability is well above the suitabilitythreshold.

Counter example C-1, with the low molecular weight polyisobutylene(Oppanol B10), on the other hand exhibits severe peel increase withpolar substrates, and also considerable residues of adhesive both afterexposure to heat and even with relatively brief exposure to UV. Thecohesion of the self-adhesive composition with this fluid type of PIB isinadequate. Furthermore, a barely visible deposit occurs on the sensiblevarnish substrate.

In counterexample C-2, the amount of Oppanol B50 is increased andthereby moved beyond the upper limit recognized as being preferred. Thisalso has the effect of weakening the cohesion. In some cases there areresidues of adhesive on the substrate after thermal exposure. Hereagain, severe peel increase is recorded, and the bond strengths afterstorage, at in some cases well above 2 N/cm, are no longer compatiblewith the application.

1. A self-adhesive composition comprising hydrogenated block copolymers or a mixture of such, comprising polymer blocks formed from vinylaromatics (A blocks) and polymer blocks formed by polymerization of 1,3-dienes (B blocks), the self-adhesive composition being blended with 10 to 80 parts by weight of polyisobutylene having a weight-average molecular weight M_(w)>200 000 g/ mol, based on 100 parts by weight of the block copolymers.
 2. The self-adhesive composition of claim 1, wherein the vinylaromatics are styrene or are based on C₈ to C₁₂ aromatics.
 3. The self-adhesive composition of claim wherein the B blocks are formed by polymerization of butadiene and isoprene or their hydrogenation products.
 4. The self-adhesive composition according to claim 1, wherein the block copolymers are hydrogenated predominantly in the middle block.
 5. A protective film comprising a self-adhesive composition comprising hydrogenated block copolymers or a mixture of such, comprising polymer blocks formed from vinylaromatics (A blocks) and polymer blocks formed by polymerization of 1,3-dienes (B blocks), the self-adhesive composition being blended with 10 to 80 parts by weight of polyisobutylene having a weight-average molecular weight M_(w)>200 000 g/mol, based on 100 parts by weight of the block copolymers, the self-adhesive composition being applied to at least one side of a carrier film.
 6. The protective film of claim 5, wherein the carrier film is a polyolefin film.
 7. The protective film of claim 5, wherein the thickness of the carrier film is between 20 and 80 μm.
 8. The protective film of claim 5, wherein the carrier film comprises at least one light stabilizer in an amount of at least 0.15% by weight.
 9. The protective film of claim 5, wherein the UV transmittance of the protective film in the wavelength range from 290 to 360 nm is below 1%.
 10. (canceled)
 11. (canceled)
 12. A process for producing a protective film of claim 17 comprising simultaneously coextruding the self-adhesive composition, carrier layer, and auxiliary layers.
 13. The self-adhesive composition of claim 1 wherein the composition is blended with between 10 to 40 ppw of polyisobutylene.
 14. The self-adhesive composition of claim 2 wherein the vinyl aromatics are based on α-methylstyrene-containing aromatic blocks.
 15. The self-adhesive composition of claim 1 wherein the B blocks are formed by polymerization of isobutylene.
 16. The self-adhesive composition of claim 4 wherein the block copolymers are completely hydrogenated in the middle block.
 17. The protective film of claim 7 comprising an adhesion promoter layer disposed between the carrier layer and the self-adhesive composition. 